1. Field of Invention
This invention relates to a method for permanently and decoratively enhancing surfaces of preformed polyethylene articles, and to a decorative enhancement composition useful in the method.
2. Brief Statement of the Prior Art
Available prior art reveals methods practiced during molding of polyethylene articles to enhance their surfaces by precoating of the mold, or by using multiple molding steps. U.S. Pat. Nos. 4,252,762 and 4,519,972 disclose methods for imparting a decorative pattern to the inside of a mold cavity which transfers to the product during the molding process. Similarly, U.S. Pat. No. 4,548,779 discloses a two-stage rotational molding process to form a product with inner and outer layers. U.S. Pat. No. 4,681,712 discloses electrostatically coating the inner surface of a mold which is subsequently charged with thermoplastic material to form a molded thermoplastic product to which the coating transfers during molding. The aforementioned processes unavoidably increase the molding cycle time, particularly when two or more molding steps are required.
A distinct disadvantage of articles formed of polyolefins, particularly of polyethylene, is their low receptivity to coatings, paints, inks, and the like. Some attempts have been made to chemically or physically treat the surfaces of polyethylene articles before applying a color coating. An example is the flame treatment of polyethylene surfaces to render them receptive to printing inks. These procedures are costly and do not result in a molded product in which the pigments or dyes of the coatings are incorporated into the molded skin of the polyethylene article, thus permitting the coating to become obliterated with wear.
It is an objective of the invention to provide a method for permanently decorating the surface of a preformed articles of polyolefin, particularly of polyethylene.
It is a further objective of the invention to provide a decorative enhancement composition for permanently decorating a surface of a preformed polyolefin article, particularly a polyethylene article.
It is likewise an objective of the invention to provide a method for protecting the decorative enhanced surface by incorporating a protective coating into the surface with the decorative coating.
The surfaces of preformed polyolefin articles, particularly polyethylene articles, are permanently colored with a decorative enhancement composition which comprises a mixture of a colorant with a particulate thermoplastic, such as polyethylene. The decorative enhancement composition is applied to the article to coat the polyolefin surface and the coated surface is heated to fuse the coating into the surface of the preformed polyolefin. The method is facilitated by incorporating a binder in the decorative enhancement composition which temporarily binds the colorant and thermoplastic to the surface of the polyolefin. The mixture of thermoplastic, colorant and binder is dispersed in a liquid carrier and blended to a uniform consistency suitable for application by spraying, dipping, brushing, etc. Multiple enhancement effects can be accomplished by applying multiple coatings of decorative enhancement compositions. A clear overcoat composition comprised of particulate thermoplastic, binder solid, and liquid carrier can also be applied to the enhanced areas of the article to enhance the permanent retention of the colorant.